Disk fails and the database goes down

	Chapter 2: Understanding Oracle Database Architecture	39
	The general rule is that you don’t want to switch log files more often than every 15–30 minutes. If you find that happening, consider increasing the size of each group.

We commonly get this question: “If my disks are mirrored at the hardware level, do I need more than one member on each group? After all, if a disk fails, I have another one right there to pick up the slack.”

Unfortunately, you get different answers depending on who you ask. Ask us, and we’ll recommend at least two members for each group:

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	Archive log files are simply copies of redo log files. They’re no different from redo log files except that they get a new name when they’re created. Most archive log files have the extension .ARC, .ARCH, or .LOG. We try to use .ARC as that seems most common.

✓I/O cost: The ARCn process has to copy each redo log group as it fills up.

✓CPU cost: It takes extra processing to copy the redo logs via the ARCn process.

	Like control files and redo log files, it’s best practice to have more than one copy of each of your archive log files. They should go to two different desti-nations on different devices, just like the others. You can’t skip over a lost archive log.

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